1. Field of the Invention
This invention relates to a projection device using a so-called index distribution type lens array in which the refractive index varies continuously.
2. Description of the Prior Art
Various projection devices in which a number of lenses having a refractive index distribution in a direction orthogonal to the optic axis are disposed proximate to one another and which forms the image of an object on a predetermined surface are known as reading apparatuses of facsimile, imaging optical systems of copying apparatuses, and the like. Particularly, index distribution type lens arrays having an erect one-to-one magnification imaging action are widely used because the distance TC between an object and the formed image thereof is short to enable an optical system to be made compact.
In apparatuses using these index distribution type lens arrays, there is a strong desire to shorten the distance between the object and the formed image thereof to make the apparatuses more compact. On the other hand, in a copying apparatus, a facsimile apparatus or the like, the distance between the original carriage and the end surface of the lens array must be a predetermined length or more from the necessity of illuminating the original carriage by an illuminating system. To meet these two requirements which are contrary to one other, it would occur to mind to form the lens array by the use of a medium in which the refractive index difference .DELTA.n between the central portion and the marginal portion of the index distribution type lens is great and the refractive index gradient is sharp, but there has been a technical limit in making a lens having great .DELTA.n.